In antenna applications such as fixed wireless access where suppression of all signals other than those in the main forward beam pattern or front lobe is desirable, auxiliary antennas are often used alongside the main antenna to enable the cancellation of side lobe interferers. The auxiliary antenna should ideally have a radiation pattern identical to the main antenna radiation pattern, but without the front lobe. By subtracting the auxiliary antenna signals from that of the main antenna, the resulting signals would then be from the main antenna's front lobe only, side lobe signals from the main antenna being cancelled by the auxiliary antenna signals.
As is known, auxiliary antennas approximating the radiation pattern or mask of a vertically polarised main antenna, minus the front lobe, can be created using a pair of vertically oriented dipoles connected in anti-phase. The two dipole radiation patterns interfere with one another to produce a pattern with relatively high gain at the side lobes and low gain in the front and reverse direction. This pattern can then be substructed from that of the main antenna to leave substantially only the main antenna front lobe To obtain a horizontally polarised side lobe canceller, this anti-phase dipole arrangement can be rotated by 90.degree. to the horizontal. However this produces nulls at +/-90.degree. to the front lobe, which severely limits this arrangement's ability to produce an approximation of the main antenna's radiation pattern less the front lobe.
U.S. Pat. No. 5,152,010 to Talwar discloses a two antenna system comprising an omni-directional main antenna and an auxiliary antenna. The auxiliary antenna of this system however provides only a rough approximation of the required main antenna side lobe pattern. The arrangement is also not well adapted for horizontally polarised main antennas.